Radio receiving apparatus



Aug. 7, 1934.

L. L. DE KRAMOLIN RADIO RECEIVING APPARATUS Filed May 29, 1929 I 5 Sheets-Sheet l 57 ms ATTORNEYS 1934- L. DE KRAMOLIN 1,969,209

RADIO RECEIVING APPARATUS File M y 29, 1929 3 Sheets-Sheet 2 BY H/S ATTORNEYS 1934- L. DE KRAMOLIN 1,969,209

RADIO RECEIVING APPARATUS Filed May 29, 1929 5 Sheets-Sheet 3 Patented Aug. 7, 1934 UNITED STATES PATENT OFFICE RADIO RECEIVING APPARATUS Lon Ladislas de Kramolin, Berlin-Pankow,

Germany 13 Claims. (Cl. 250-20) The invention relates to radio receiving apparatus and has for its object to provide an improved circuit arrangement enabling a radio receiving apparatus to be constructed capable of receiving signals from different transmitting stations with the minimum of manipulation.

An object of the invention is to provide a radio receiver having a single tuning element which nevertheless is efficient and stable.

Another object of the invention is to reduce the cost of receiving apparatus by constructing the screening element or elements'so that they serve as supports for the radio tubes and other components.

-A further object of the invention is to provide a radio receiving exchange, which enables any station of a plurality of transmitting stations to be selected at will and received on the apparatus by merely throwing the particular switch associated with the station desired.

The invention is illustrated in the ing drawings wherein:

Fig. 1 is a diagram of a novel superheterodyne circuit.

Fig. 2 is a diagram illustrating the tuning elements and the switches for selecting a particular value of capacity to be connected in the receiving circuit.

Fig. 3 shows a perspective view of a complete set. 1

Figs. 4-5 show the improved method of constructing the case for the receiver.

Figs. 6-8 show constructional details of the change over. switches and arrangement of conaccompanydensers in the radio exchange.

As mentioned in the specification of my previous application Serial No. 322,426, it is preferable when employing aperiodic or semi-aperiodic coupled aerial circuits to rectify the incoming oscillations by operating the input tube as a commutator tube (that is, in such a manner that it short circuits an external circuit connected between the grid and filament, once every cycle in cadence with locally generated oscillations) than to superpose the said incoming oscillations on those locally generated and subsequently rectify the resultant oscillations. With the latter method it is possible for a large number of frequencies to reach the input grid of the first tube in an ordinary superheterodyne arrangement due to the aperiodic aerial coupling, which frequencies, after they are compounded with local oscillations and rectified, produce a number of troublesome resultant frequencies which distort reception. In

the arrangement described in the above mentioned specification, the commutator effect in the input or mixing tube is only imperfectly achieved because one and the same grid is employed for generating the local oscillations andfor picking up the received waves as well as for producing the commutator effect. As a result of this, only partial rectification occurs which is accompanied by the above mentioned disadvantages. These disadvantages may be overcome if the input tube is provided with a number of grids.

In the circuit diagram illustrated in Fig.1 by way of example, the local oscillations are produced in the circuit 6, 7 by reason of the coupling between the coil 6 and the coil 8 connected in the anode circuit of the mixing tube 1. The local os-' cillations are conducted to the grids 9 and 10 respectively situated on either side of the input grid 11. The grids 9 and 10 receive a positive voltage amounting to approximately half the anode voltage. Due to the coupling between the anode coil 8 and the coil 6 of the oscillatory circuit, the positive voltage and the local oscillatory voltage are compounded in every half cycle of the local oscillations and powerful amplification of the wave hand picked upby the antenna during this period is obtained, whilst in the succeeding half period these two' voltages counteract and nullify one another thus cutting ofi the tube and stopping its action. The tube therefore acts in a much more complete manner to produce a commutator or switch eflect similar to that produced in the input tube of the arrangement described in my above application.

In order to secure eflicient operation of the apparatus, the intermediate frequency which results when the incoming and locally generated oscillations are compounded should be chosen so that it is not too far removed in the frequency spectrum from the band of waves to be received, so that waves within this band when compounded with locally generated oscillations will .only produce one resultant frequency. For example, a frequency of approximately 461.5 k. c. may be selected since this frequency in view'of the above stipulation is suitable both as regards the short wave range 1500 k. c. to 500 k. c. and the long wave range'375 k. c. to 150 k. c. The frequencies which the local oscillator must provide will therefore be 961 k. c. to 1,961 k.-'c. for the short wave range and 836 k. c. to 611 k. c. for the long wave range. The use of a comparatively low intermediate frequency has the advantage of avoiding excessive cutting of the side bands.

The input circuit comprises two band pass-- filters 12 and 13 either of which may be connected to the grid circuit of the mixing tube. One of these filters is adapted to pass the low wave band between the limits indicated, and the other the high wave band. For changing from one wave range to the other, the switch comprising mechanically coupled switch arms 14, 15 and 16 is moved so as to connect up either one band filter or the other as desired. Simultaneously, the switch arm 14 either adds to or removes the windings 17 from the coil 6, thus altering the inductance component of the circuit 6, 7 and thereby the frequency of the locally generated oscillations. The variable condenser '7 in this circuit is then adjusted to tune in a particular transmitter.

The intermediate frequency obtained from the tube 1 is then passed to an amplifier as shown in Fig. 1 comprising stages 2, 3 and 4, the grid circuits of which may be tuned to give selectivity. The stage 3 comprises two three-electrode tubes in push pull, the output of which is connected to the stage 4. The amplified oscillations thus obtained in the tuned anode circuit of the tube 4 are passed to the grid of a detector tube 5 to which a grid condenser 18 and a grid resistance 19 is connected, a telephone or any suitable reproducing instrument T being connected in the anode circuit thereof. The anodes of the tubes are fed the leads 1 to 5, the current and the grid bias being supplied through leads LT+ to G5.

It is to be understood that any suitable amplifier may be employed in connection with the mixing tube and that the amplifier illustrated in.

the drawings is only shown by way of example.

As is well-known amplifiers when connected in cascade tend to oscillate and it is therefore desirable to employ screened grid tubes in order to maintain stability. If high amplification is desired, in which case even a screened grid tube amplifier becomes unstable, then frequency doubling stages may be employed. In this manner very high amplification can be obtained without distortion due to instability. Since only one variable condenser is used in the oscillatory circuit 6, 7 for tuning, a number of fixed condensers can be connected in parallel with the coil 6 in place of this condenser. The value of these condensers can be fixed in such a manner that when one or a number of them are inserted into circuit, a wave of known frequency will bev received.

These condensers may 'be adjusted to the exact capacity value by means of a set screw or the like, and they may be connected into circuit by means of push button or snap switches. By this means the tuning of the apparatus can be greatly simplified as it is then only necessary to move the wave change switch 14, 15, 16 and to press a button or combination of buttons to receive a certain transmitter.

In Fig. 2 the inductance in the tuning oscillatory circuit is represented by 6. .The tuning condenser is shown composed of fixed condensers 7 arranged so that they can be connected in parallel to inductance 6. Each fixed condenserhas a small variable condenser '7" connected in parallel to it for the purpose of the adjustment above mentioned. The push buttons are adapted to actuate switch contacts 7' thus connecting the condensers to the inductance 6. A variable condenser may be provided for the purpose of accurately adjusting the capacity value and thus giving exact frequency response to the transmitter which it is desired to receive.

The general construction of the case for the simple means for obtaining electrostatic screening of the elements of the receiver, whilst at the same time providing a rigid construction and keeping permanently protected those elements which do not, normally, require removal. According to the present construction the usual complicated screening arrangement is simplified by forming the screen member as the carrier or body of the whole apparatus.

Referring to the Figures 4 and 5, 20 and 21 represent two metal plates which divide the rectangular hollow space formed by the box into two compartments, in the lower one of which are arranged the condensers andother firmly mounted parts which can 'be attached to its walls, whilst the upper compartment accommodates the tubes and other similar replaceable parts. The two plates 20 and 21 may, if desired, be constructed from one piece of metal. By means of the partitions 22, a further division of the casing into separate compartments may be made, in order to extend the use of screening. At the same time, these partitions serve also for supporting or stiff ening the casing so that an absolutely firm structure results.

In the case of the radio exchange, the changeover contacts and associated condensers are preferably arranged above this screening box, as shown, and themselves also screened. by a further metal plate 23, electrically connected with the screening box 20, 21.

In order to obtain a compact exchange, the change-over contacts and associated condensers are preferably arranged andoperate as shown more clearly with reference to Figs. 6 and 7.

In these figures, 24 represents a push-button which when pushed in forces the contacts 25 and 26 apart to engage with bus-bars 27 and 28 respectively, which are connected with the tuning system of the receiver as hereinbefore described. 29 and 30 are the fixed and variable condensers respectively which correspond to the fixed and variable condensers 'l and 8 respectively as shown in Figure 2. The values of the variable condensers may be easily adjustedby turning the screws 31 whereby the plates 32 and 33 of the condensers are brought closer together. The plates are insulated by a mica strip 34. The fixed condensers 29 are mounted in a staggered fashion, as shown in Fig. 8, so that the complete arrangement is very compact. In pushing in the push button 24, the member 35, common to all the push-buttons, is lifted and then drops back, by means of the spring 36, behind the detent 37 to hold the push-button in the operative position. On pushing another button, the button already in the operative position is released by the lifting of the member 35 and is returned to its normal position by the spring 38. For tuning in those stations which are not logged on the exchange,- the main condenser 39 may be used in conjunction with one or more of the push-buttons 24 which, when operated, insert this condenser 39 in the tuning circuit.

When the complete apparatus is assembled, the N variable condensers 29 may be adjusted by means through the holes 40 in the top meansforcompoundinglocal and incoming oscilla- 1 tions comprising a thermionic device, and switchingmeans adapted to connect any one of said bandpass filters to the input grid of said device, said oscillatory circuit comprising variable inductive and capacitive components, said inductive component having a plurality of values, any one of which may be associated through said switching means with any one of said band-pass filters, said capacitive component being variable within limits defined by said inductive values for accurately heterodyning the oscillations produced by said oscillatory circuit with any frequency passed within the limits defined by said band-pass filter, said capacitive component being varied by a plurality of pre-tuned condensers any one of which may be connected into circuit by independent switching means.

2. A radio receiver comprising a cabinet, electrostatic screening means arranged within said cabinet, a plurality of band-pass filters associated with an antenna, a local oscillatory circuit, means comprising a plurality of capacitive elements any one of which is adapted to be connected into circuit for varying the response frequency of said oscillatory circuit, means for connecting any one of said band-pass filters into circuit, a plurality of push button switches one of which is associated with each capacitive element, means for accurately fixing the value of said capacitive elements, a tuned amplifier and detecting means, the components being mounted upon said screening means in said cabinet, said screening means dividing the cabinet into two compartments, the permanent components being enclosed in one of said compartments while the interchangeable components are easily accessible.

3. A radio receiving apparatus comprising in combination a cabinet, electrostatic screening means arranged within said cabinet, said screening means extending behind the front, a part of the top, a part of the back and across the interior of said cabinet, a plurality of band-pass filters, associated with an antenna, a thermionic device having an anode, a cathode and a number of grids, switching means for connecting any one of saidband-pass filters to one of the grids, an oscillatory circuit associated with the other grids and the anode circuit of said thermionic device, said thermionic device being arranged so that it is rendered inoperative once in every cycle of oscillations produced by said oscillatory circuit, whereby oscillations conducted through said pickup circuit and said locally generated oscillations are compounded in the anode circuit of said device as beat oscillations, said oscillatory circuit comprising variable inductive and capacitive components, said inductive component having a. plurality of values any one of which may be associated through said switching means with any one of said band-pass filters; said capacitive component being varied by a plurality of pre-tuned fixed condensers, any one of which may be connected into circuit for varying the response frequency of said oscillatory circuit, a plurality of push button switches one of which is associated with each of said condensers, means for accurately fixing the value of said condensers, means comprising a tuned amplifier for amplifying said heat oscillations and means for detecting and rendering said oscillations audible.

4. In a radio receiver, the combination of a semi-aperiodic pick-up circuit comprising a plurality of band-pass filters, a thermionic device having an anode, a cathode and a number of grids, switching means for connecting any of said band-pass filters to one of the grids, means comprising an oscillatory circuit associated with another of' the grids and the anode circuit of the device, whereby oscillations conducted through said pick-up circuit, and those produced by said oscillatory circuit are compounded in said anode circuit as beat oscillations, means comprisinga switch associated with one of the coupling coils of said oscillatory circuit for varying the frequency of the oscillations produced thereby, and means mechanically coupling said filter switching means with said coupling coil switch for operating both of said switching means each in dependence upon the other.

5. Thermionic frequency changing apparatus for superheterodyne radio receivers comprising in combination a thermionic device having an anode, a cathode and three grids between'said anode and cathode, means for, producing oscillations connected between the two outermost grids con nected together and the cathode of the tube, signal oscillations being conducted to the centre grid, the compounded oscillations being collected in'the anode circuit of the tube.

6. In a radio receiver, the combination of a semi-aperiodic pick-up circuit comprising a plu rality of band-pass filters, a thermionic device having an anode, a cathode and a number of grids, an oscillatory circuit comprising an inductive and a capacitive component connected between one of said grids and the cathode of the tube, switching means associated with said inductive componentto vary the inductance thereof, switching means for connecting any one of said band-pass filters to another of the grids, and a mechanical coupling between said two switching means whereby each of said band-pass filters is associated with a particular value of said inductive component, said capacitive component being variable within limits defined by said inductive values for accurately heterodyning the oscillations produced by said oscillatory circuit with any frequency passed within the limits defined by the associated band-pass filter to produce a predeter mined intermediate frequency. 7. In a radio receiver, the combination of a semi-aperiodic pick-up circuit comprising a plurality of band-pass filters, a thermionic devicehaving an anode, a cathode and Ya number of grids, an oscillatory circuit comprising an inductive and a capacitive component connected between one of said grids and the cathode of the tube, switching means associated with said inductive component to vary the inductance thereof, switching means for connecting any one of said band-pass filters to another of the grids. and a mechanical coupling between said two switching means whereby each of said band-pass filters is associated with a particular value of said inductive component, said capacitive component comprising a plurality of pre-set capacitive elements and means for connecting any one of said elements into circuit by independent switching in circuit, and switch means associated with a frequency determining component of said local oscillator circuit, for varying the frequency of the oscillations produced thereby.

9. In a radio receiver, the combination of a semiaperiodic pick-up circuit comprising a plurality of band-pass filters, a thermionic device having ananode, a cathode and a number of grids, switching means for connecting any one of said band-pass filters to one of the grids, an oscillatory circuit comprising capacitive and inductive components associated with another of the grids and the cathode of the device, whereby oscillations conducted through said pick-up circuit and those produced by said oscillatory circuit are compounded in the anode circuit of the device as beat oscillations, and means comprising a switch associated with the inductive component of said oscillatory circuit for varying the frequency of the oscillations produced thereby.

. -l0. In a radio receiver, the combination of a semi-aperiodic pick-up circuit comprising a plurality of band-pass filters, a thermionic device having an anode, a cathode and anumber of grids, an oscillatory circuit comprising an inductive and a capacitive component connected between one of said grids and the cathode of the tube, switching means for connecting any one of said band-pass filters to another of the grids, said capacitive component comprising a plurality of pre-set capacitive elements and means for connecting any one of said elements into circuit by independent switching means.

'11. Thermionic frequency changing apparatus for superheterodyne radio receivers, comprising a, thermionic device having a cathode, an anode and a plurality of grids, means for applying signal oscillations between the cathode and one of said grids, means for applying locally generated oscillations between the cathode and another of said grids and means for so'biasing said grids that the device operates with a linear grid voltage/anode current characteristic, said signal oscillations and locally generated oscillations being compounded in the anode circuit of the device.

12. Thermionic frequency changing apparatus for superheterodyne radio receivers, comprising a thermionic device having a cathode, an anode and at least three grids therebetween, means for applying incoming oscillations to one of said grids, means for applying locally generated oscillations to grids connected in parallel and situated on either side of said first named grid, and means,

erated oscillations to the grids on either side of said centre grid and means for applying a low biasing voltage to' said centre grid and a high biasing voltage to'said other grids, whereby the device is caused to operate with a linear grid voltage/ anode current characteristic, to cornpound the oscillations in said input circuit with said locally generated oscillations.

LEON LADISLAS nr: KRAMOLIN. 

